Distillation is the most common separation process used in the chemical, petrochemical, refining and related process industries. It consumes a large amount of energy due to the heating and cooling steps involved through the reboiler and condenser respectively. The major cost overhead for the process industries comes from operating costs which includes raw materials cost, energy cost and labor cost. It would be desirable to reduce the energy cost in the interest of economy as well as society.
There are complex distillation configurations available which offer substantial reduction in energy and capital expenditures. These options include, but are not limited to, dividing wall columns and thermally coupled columns.
Although thermally coupled columns require 20-30% less energy, they have serious drawbacks that make them ineffective for commercial installations. For example, thermally coupled arrangements are realized by setting up two-way vapor/liquid flow between different columns of a distillation sequence. One of the drawbacks of thermal coupling is non-uniform vapor liquid traffic in the column. As shown in FIG. 1, the top and bottom section of the column sees heavy vapor liquid traffic, whereas in prefractionation and main section, of the column the traffic is low. The heavy traffic puts a restriction on column capacity and in many cases existing column shells cannot be utilized.
There is therefore a need to develop and implement a thermal coupling system that has superior energy conservation properties, while at the same time having a uniform vapor liquid traffic in the column.